The use of electric motors/generators in a number of application areas is known. For example, in self propelled devices, pumps, and/or power generation. Traditional electric motors/generators typically work reasonable well at particular speeds and power requirements. However, as the speed or power output is varied the efficiency of these traditional motors/generators drops. To ensure that the device keeps operating at high efficiency most devices are often run at higher speeds even when less would suffice, wasting energy, or are coupled to expensive and heavy transmission systems which require ongoing maintenance and greatly increase the number of moving parts increasing the risk of failure.
Modifying existing motor drive systems such that they are capable of Adjustable Speed Drive (ASD) can introduce energy savings depending on the application. However, adding ADS to traditional motors is an expensive exercise. The power supply's frequency has to be modified, requiring high current switching, which use large and expensive electronic switches. Further once the speed of the motor is adjusted the motor may no longer be operating at its peak efficiency therefore the energy savings of running the motor slower may be offset by running the motor in a region that is less efficient.
Various configurations of traction electric motors are known. However, for many applications such motors tend to have excessive weight and bulk. Also known is the use of disk-shaped wheel motors, located at or within a wheel, and driving directly. At present, the majority of traction motors used, for example, in hybrid electric vehicles (HEV) and electric vehicles (EV) are interior permanent magnet synchronous machines. In common with other synchronous designs, these may suffer from conduction and magnetic losses and heat generation during high power operation. Rotor cooling is more difficult than with brushless direct-current motors and peak point efficiency is generally lower. Generally speaking, induction machines are more difficult to control, the control laws being more complex and less amenable to modelling. Achieving stability over a suitable torque-speed range and controlling temperature is more difficult than with brushless direct-current motors. Induction machines and switched-reluctance machines have been used for many years, but require modification to provide suitable optimal performance in, for example, HEV and EV applications.
In an application such as wind powered electric generation, these systems tend to be bulky and costly to repair. They also typically require a gear box, a motor, an inverter and/or a transformer making them fairly complex systems that are subject to greater chances of malfunction.
There is a need for improved systems, devices and methods directed to electric motors/generators. The present disclosure is directed to overcome and/or ameliorate at least one of the disadvantages of the prior art as will become apparent from the discussion herein.